It is well known that aspartame (APM) sweetened chewing gum products are susceptible to decomposition and/or reaction of the APM under certain conditions, causing loss of sweetness and undesirable off-flavors. The conditions that contribute to the decomposition and/or reaction of APM include, but are not limited to, exposure to heat or moisture, a neutral or alkaline pH, and the presence of aldehyde-containing flavoring agents. Under these conditions, APM can hydrolyze to the dipeptide aspartylphenylanaline (AP), or decompose to diketopiperazine (DKP), or react with aldehydes. AP and DKP can decompose further over time to their individual amino acid components.
AP and DKP, and their decomposition products, are not sweet and impart undesirable flavors to chewing gum. Therefore, it is necessary to control the decomposition of APM. Since APM cannot tolerate high temperatures for extended periods of time, the production of chewing gum containing APM must be accomplished relatively quickly and using as low a temperature as possible, with the APM added late in the mixing process during the driest part of the mixing cycle. Generally, APM has relatively good stability at a pH between about and 5, with optimal stability occurring at about pH 4.0-4.3. However, some chewing components, especially gum bases containing calcium carbonate filler, typically cause chewing gum to have pH's above that range.
Methods have been employed to attempt to stabilize APM, thus reducing its decomposition and reactivity in a chewing gum environment. For instance, Glass et al. U.S. Pat. No. 4,822,621 discloses a technique in which the APM and the flavoring agent are initially blended into two separate gum portions, which are then coextruded together. Prior to chewing of the gum, the contact between the APM and the flavoring agent is generally limited to the interface between the coextruded portions.
Shoaf et al. U.S. Pat. Nos. 3,298,633 and 3,956,507, disclose a technique in which the APM is dispersed in a hot melt and the hot melt is cooled, thereby encapsulating the APM. Examples of hot melt ingredients include anhydrous and hydrous citric acid. Other fusing agents include monosaccharides, polysaccharides and other materials. These references deal only with food and beverage applications.
Demaso et al. European Application 0 134 322 discloses that a low pH, preferably in the range of 2-3, is the most desirable for APM stability. The reference deals only with a process for incorporating APM into extruded food products including cereals and baked goods.
Klose et al. U.S. Pat. No. 4,246,286 discloses the stabilization of APM in a chewing gum composition, by adjusting the chewing gum pH to between 5.0 and 7.0. This is accomplished by eliminating calcium carbonate filler from the gum. Also, citric acid or another non-toxic organic acid is employed as an acidifying agent.
Japanese Publication Sho 61-212255 discloses a sweetener composition containing APM, fructose and small amounts of organic acid and organic acid salts. The organic acid is selected from citric acid, tartaric acid, malic acid, fumaric acid and adipic acid.
U.S. Pat. No. 4,087,557, issued to Bakal et al., discloses the entrapping of artificial sweeteners other than APM in an ester gum, in order to reduce or delay the initial sweetness impact of the artificial sweetener.
U.S. Pat. No. 4,556,565, issued to Arima et al., discloses that APM in a chewing gum containing calcium carbonate does not have good long term stability because the APM is rapidly decomposed by the calcium carbonate. The reference discloses a chewing gum in which the calcium carbonate in the base is replaced with microcrystalline cellulose powder.
U.S. Pat. No. 4,064,274, issued to Mackay, discloses the use of a non-basic filler such as magnesium silicate. A fruit acid is added to the gum to bring the pH to below 4.0.
U.S. Pat. No. 4,122,195, issued to Bahoshy et al., and U.S. Pat. No. 4,139,639, issued to Bahoshy. disclose the encapsulation of APM to improve its stability.
U.S. Pat. No. 4,085,277, issued to Mackay et al., discloses a chewing gum in which a finely divided sweetening agent and a finely divided food acid are dispersed in the gum base portion thereof.
U.S. Pat. Nos. 3,928,633, 3,956,507 and 4,004,039, issued to Shoaf et al., disclose the encapsulation of APM by melting a fuseable mass and subdividing it to encapsulate the APM therein. Citric acid monohydrate, citric acid, and other food acids are employed as diffusing media.
U.S. Pat. No. 3,868,472, issued to Berg et al., discloses the co-grinding of APM with an acid, in the presence of an organic solvent in which the APM is insoluble.
U.S. Pat. No. 4,792,453, issued to Reed et al., discloses a sugarless hard coated chewing gum having a chewing gum center prepared by mixing calcium carbonate, glycerine, and an aqueous sorbitol solution, and later adding an encapsulated high intensity sweetener.
U.S. Pat. Nos. 4,774,094 and 4,753,806, issued to Carroll et al., discloses the stabilization of APM by cooking the APM in aqueous hydrogenated starch hydrolysate or, optionally, glycerine.
European Patent Application 0 272 220 and U.S. Pat. No. 4,824,681 disclose the encapsulation of APM in a coating material comprising a hydrophobic polymer and a hydrophobic plasticizer. An acidifying agent can be included in the coating material to extend the shelf life of the APM.
Japan Patent Disclosure Nos. Sho 83.198250, Sho 83-193655 and Sho 87.25014 all disclose the dispersion and encapsulation of APM in hydrogenated starch hydrolysates and/or hydrogenated maltose syrup. In the '250 reference, microcrystalline cellulose powder is used instead of calcium carbonate or talc. In the '655 reference, a combination of sodium citrate and citric, malic or tartaric acid is also used in the encapsulating agent in order to maintain a pH of [4.3 .+-. 1.0. In the '014 reference, vegetable gum is also included in the sweetener ingredient. In all of these three references, the ingredients are first dissolved and mixed in water, and then dried and powdered.
U.S. Pat. No. 4,673,577, issued to Patel, discloses the use in chewing gum of APM which has been encapsulated with a food grade shellac.
U.S. Pat. No. 3,922,369, issued to Glicksman et al., discloses the co-drying of solutions of an edible organic acid and APM.
European Patent Application 0 302 024 discloses chewing gum having APM in a first portion, and aldehyde flavoring agent in a second portion and a barrier film in between the first and second portions. European Patent Application 0 302 023 discloses a similar chewing gum except that the first portion may also contain an organic acid to help stabilize the APM.
Thus, it is known from the prior art that APM is more stable in an acid environment. The most common approach has been to place the acid in the immediate vicinity of the APM, to place and maintain the APM and acid in a dry form, and to encapsulate or otherwise isolate the APM from the humectant (i.e. moisture containing ingredients) of the chewing gum. However, because the humectant is generally required to be distributed substantially uniformly throughout the chewing gum, it is difficult to maintain this isolation of the APM while at the same time providing an even distribution of sweetness. Also, the pH in the vicinity of the APM is rather difficult to control and maintain uniformly with the range of 3.0-5.0 when the acid is concentrated in the vicinity of the APM and is not homogeneously distributed throughout the chewing gum.